Lord Livius Erimond of Vyrantium is a magister of the Tevinter Imperium and an agent of the Venatori.
On behalf of Corypheus he manipulated Warden-Commander Clarel de Chanson by offering an alliance. He convienced her to sacriface warden warriors by warden mages to bind demons, so they could become an army to invade Deep Roads and kill the Old Gods before they become archdemons. In fact that ritual binded the warden mages to his master and he kept it in secret.
In the Western Approach Erimond is confronted by The Inquisitor while instructing Grey Warden mages in blood sacrifice. Erimond's attempts to control the Inquisitor through magical manipulation of the Anchor backfire, leading him to flee to Adamant Fortress.
Erimond is pursued by the Inquisition, who lay siege to Adamant, but Erimond persuades Warden-Commander Clarel to initiate the summoning ritual. Clarel started to wonder when the Inquisitor told that Erimond is servant of Corypheus. Erimond summoned Corypheus' dragon to kill the Inquisitor, but this backfires when Clarel mistakes it for an Archdemon and concludes (rightly) that Livius Erimond sees the Blight as a tool instead of as an enemy.
Erimond is defeated by Clarel but escapes death after the Warden-Commander is devoured by the dragon. Despite the subsequent collapse of the rampart where he is situated, Erimond survived the Siege of Adamant and is brought to Skyhold for judgement.
Chained Lord Erimond is dragged to face judgement for his crimes, though he refuses to recognize the Inquisition's authority, claiming that death at their hands would be a validation, sending him to glory.